1. Field of the Invention:
The present invention relates to the improved preparation of fluorobenzenesulfonyl fluorides and, more especially relates to the preparation of fluorobenzenesulfonyl fluorides by exchange fluorination, i.e., the exchange of a fluorine atom for at least one chlorine atom comprising a chlorobenzenesulfonyl fluoride.
As used herein, by the term "chlorobenzenesulfonyl fluoride" there is intended any compound having the structural formula: ##STR1## wherein n ranges from 1 to 5 (1.ltoreq.n.ltoreq.5). Those compounds prepared according to the process of the invention have the structural formula: ##STR2## wherein the fluorine atoms are ortho- and/or para- to the SO.sub.2 F moiety, m ranges from 1 to 3 (1.ltoreq.m.ltoreq.3) and n is as defined above.
The subject process is applicable equally as well to those starting materials (I) wherein the benzene nucleus bears one or more "stable" substituents, in the conditions of the reaction e.g., a hydrocarbon substituent.
2. Description of the Prior Art:
Exchange fluorination reactions are per se well known to this art. Compare G. G. Yakobson et al, Chemical Abstracts, Vol. 63, 14740e (1965) and Chemical Abstracts, Vol. 66, 94741e (1967) wherein the molten phase reaction of p-chlorobenzenesulfonyl fluoride, 2,4-dichlorobenzenesulfonyl fluoride and 2,4,5-trichlorobenzenesulfonyl fluoride with potassium fluoride is described, same being conducted at temperatures varying between 240.degree. and 290.degree. C. for 25 to 40 hours to respectively obtain p-fluorobenzenesulfonyl fluoride, 2,4-difluorobenzenesulfonyl fluoride and 5-chloro-2,4-difluorobenzenesulfonyl fluoride, in the respective yields of 60%, 55% and 45%.
A process of this type, however, is not entirely satisfactory on an industrial scale, principally because of the elevated temperatures that must necessarily be maintained over very long periods of time.
Cf. French Pat. Nos. 1,360,917 and 1,446,914; Barbour et al, Industrial and Engineering Chemistry, Vol. 58, No. 1, 48-55 (1966).